I may be aquiring yet another betta from a friend who can't take care of him. If I do I will have 4. When I move into my own house this summer I want to set up a 10gal tank with dividers. They would each have 2.5 gallons, which is more than they have now. Right now they are in 1.5 gallons. Would that many in a tank that size be ok?

The shape of the compartments is what I'm not a fan of. A 10 gallon tank is 20 inches long, so each compartment would have less than 5 inches, when accounting for dividers. You'll get almost a full 7 inches apiece if you only split it into three.

I may do two of the 5 gallons. I'm still undecided about this fourth fish. My friend has him in a tiny bowl and says hes not active so I told her what to do to keep him happy and she'd rather just give him away than go buy new things for him. I feel bad for him and would like to take him in I just don't want to overrun my aunts house with tanks! Granted they will all be in my room so they don't have to see them if they dont want to...such a decision lol

I personally wouldn't recommend splitting a ten gallon between four fish. If you do decide to do it, make sure you get colored mesh instead of a clear divider. If you have particularly aggressive male bettas, they can really stress themselves out if they can see the others on the opposite side of the mesh. I had that problem between my two boys and ended up doubling up on some black crafting mesh just to calm them down. Also, you'll have to make sure the water is filtering throughout the whole tank unless you want to buy multiple filters.